1. Technical Field
This invention relates to the art of making lightweight disk brake rotors, and more particularly to the technology of enhancing the wear life of the disk brake assembly utilizing such rotor.
2. Discussion of the Prior Art
For weight reduction of vehicles, it is desirable to be able to use lightweight metals, such as aluminum, magnesium, or metal matrix composites using such metals as the matrix, in brake structure applications such as rotors and drums. Unfortunately, aluminum and many of its alloys as well as other lightweight metals, when used as brake drums or rotors, result in unacceptable wear of the braking surface material that is brought to bear against the brake lining or disk brake pads. Such wear often promotes unpredictable braking characteristics. In the case of lightweight or aluminum brake drums, the problem has been addressed by use of preformed grey cast iron liners of substantial thickness of about 1/4 inch which are integrally bound to the aluminum or lightweight drum when it is cast (see SAE Paper 710247, "Influence of Rotor Metallurgy on the Wear of Friction Materials in Automotive Brakes", S. K. Rhee, 1971; and SAE Paper 780248, "Aluminum Structural Castings Result in Automobile Weight Reduction", B. E. Hatch et al, 1978).
However, disk brake rotors constructed of aluminum or lightweights materials cannot accept such preforms and have not been introduced commercially because of the poor wear life of the braking surface and because high heat transfer to the lightweight metal causes thermal distortion and other stress problems under certain critical braking conditions. Thus, the issues that remain are essentially threefold: how to (a) provide an outer face for the rotor disk that enhances the wear life of the braking surface which bear against the friction pads; (b) ensure strong bonding of such face with a lightweight metal rotor; (c) provide a rotor construction that inhibits heat transfer of the braking forces heat buildup to the lightweight metal rotor during the most extreme braking conditions.
Metal sprayed coatings or facings applied to heavy metal rotors such as steel provide a more uniform and enhanced coefficient of friction, but do not solve the threefold problem above (see U.S. Pat. No. 4,351,885).